Does a ROW car need a bump steer kit?
 

I just picked up a bumpsteer kit, the simple one that uses spacers to lower the steering box. But then I started thinking, my car is a gray market ROW car. It should have come from the factory set up for the lower height. I do notice that I get a fair bit of bump steer, but this might be a function of the larger tires as well?

84 ROW nonsunroof Carrera. Running 205-50-17 on cup II wheels.

All this started because of the ER site showing all the parts needed in a sport performance 2 kit. I thought ha, I can save $25 by not buying the bumpsteer kit at least.

I'm sure the suspension is stock, and 32 yrs old. See photos below

http://forums.pelicanparts.com/uploa...1482227409.JPGhttp://forums.pelicanparts.com/uploa...1482227509.JPG

Afaik there are no geometry changes between US market and ROW cars. Euro height (true Euro height, not the lowered cars people like to claim is Euro) is actually the geometry the cars are designed around.

Kind of a moot point with your car either way, as from MY83 on, US and Euro height were the same.

This was the special US ride height from an archived C&D road test of a '79 SC:
http://media.caranddriver.com/images...s-original.jpg

And this is Euro/ROW height from C&D 1984:
http://media.caranddriver.com/images...-s-429x262.jpg

You can visually trace the rocker panel trim line to the wheel center caps to see the difference.

We all like to go lower, even if it makes the car worse, because it looks cool.

You really can't tell from pictures. You need to measure it.

Actually you need to find a shop that has the correct equipment. Very few shops have the necessary tools and experience. Get ready to spend serious money.

http://forums.pelicanparts.com/uploa...1482241523.jpg

Here's a long thread on all of this. Search is your friend. :)

http://forums.pelicanparts.com/uploa...1482241715.jpg

Richard Newton
My Forever 911 Project

for an '84 911
front hgt spec is 108mm+/5, lowered end of spec is 113mm, this is the same as was used before uS govt got involved
rear hgt spec is 16mm+/-5, lowered end of spec is 11mm, this is 4mm raised rom the original spec od 12mm+/-5

your front tires at least are the same height as the original 205/55 x16, I''d prefer a 225/45 x17 myself but you have what you have. In any event the tires won't affect ride height od steering geometry.

The rack spacer kit is fine and appropriate for cars lowered ~10-20mm+/- from the above, if lowered much more than that other more drastic measures are indicated

Is that for REAL? Precise dial gauges AND A PIECE OF PLYWOOD??

Crude but effective. You just want to measure the changes in deflection as the suspension moves through it's travel. The plywood plate should suffice as long as the dial gauges don't move on the mounts.

Thanks Bill,
I was mostly wondering if the aftermarket bumpsteer kit is redundant, if it wasn't lowered beyond what would be considered the original spec. I still need to do a basic ride height measure and see where I'm at.
As I said, I think most of my suspension is still original.

Thanks Matt for that information. You read the forums and think you know something, but when you really start asking questions, you find out all you thought you knew was slightly skewed awry.

http://forums.pelicanparts.com/uploa...1482279770.JPG

FWIW, this is the best pic I have showing the ride height. Again with non stock wheels and tires.
Just an illustration of where I'm at.

Wouldn't a bare wheel and a steel mounting point for those magnetic gauges be a better more reliable setup?

Nope, it's been lowered...that explains the extra body roll too.


Cheers,

Joe

Just to be clear, the bump steer kit RAISES the steering rack. As the rest of the body has been lowered relative to the wheels, the rack needs to be raised to move the tie rods back into right relationship with the wheels.

Most told me to add the kit, but I went from US spec elevated ride height on my stock SC to true euro height without it and had no adverse effects. Only mod I have is turbo tie rods. YMMV

Here are the relevant curves fr a 3.2 Carrera(US and RoW have the same specs)
http://forums.pelicanparts.com/uploa...1482447318.jpg
the bump steer curve is vorspur, Vorderachse, this is the front toe curve.
Ideally it would be a vertical line, it's ok down to ~45°, the more it goes down from 45° the more unacceptable bump steer becomes

Ya know, as I was trying to explain what a bumpsteer kit did to my SO, I realized that lowering the steering box would be going in the wrong direction. So I had stumbled onto the correct answer by chance. But RDM, thanks for that quick shot of insight.

Joe,
So you think it's been lowered which I agree it looks like it. But then the body roll, are you saying because the suspension is 32 yr old, or because it's been lowered.

Bill,

Interesting graph. To put it for me into even more perspective, what do you think is the actual travel in mm of a lowered suspension on street or track with let's say 21/29 torsion bars? So that I have an idea at what level it leaves that still ok 45° toe-in curve. Travel=Radhub.

It's hard to say, my car is lowered to the red line and has a rack spacer, the rack spacer moves the dashed curve up by the thickness of the spacer which I think is 10mm
http://forums.pelicanparts.com/uploa...1482604390.jpg

Look under the front of your car at the angle of the A-arms. They should be angled slightly downward from the center to the outer ends where the ball joints attach.

If the front suspension is lowered to the point where the A-arms are angled up, such that they are higher on the ball joint end than in the middle your roll stiffness will be much less.

Let us know how much the rack spacers help your handling.

BTW, If you are going to autocross much you should be thinking about larger torsion bars. With sticky tires the cornering forces are much greater than what these cars experienced when designed as street cars. With stickier tires the only way to control body roll and pitch,is to up the torsion bar size.

No one makes large enough sway bars to control body roll on a 911?

I'm asking because I ran into the same problem with a Corvette. No one made a large enough sway bar so GM Engineering told me to use stiffer springs. It worked. As GM said at the time "We don't live in an ideal world."

Richard Newton

I know a guy who is running 31mm front sways on an SC. The problem isn't just body sway. It is also pitching. The front to rear up and down motion needs to be held in check as well as the side to side motion.

I, and I'm sure others, learned the hard way that just slapping on large sways can't optimize handling. The problem occurs when you are braking going into a turn. The front goes down on to the stops and the rear raises up as you enter the turn. Your suspension is out of its optimal operating range and being on the stops causes the spring rate to be off the chart. The result is a car that will under steer badly on entry then over steer. Then as you exit the turn under power the opposite occurs. The car plows as the front lifts and the rear squats down on to the stops.